JP2010258065A - Light-emitting device and electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce errors in the light quantity of a light-emitting element for each drive circuit. <P>SOLUTION: A light-emitting device 100 is provided with a plurality of unit circuits U and a plurality of drive circuits 22[1]-22[K], corresponding to circuit groups G[1]-G[K] into which the plurality of unit circuits U are divided. Each unit circuit U includes: the light-emitting element E, which emits light by the supply of a drive current IDR; a drive transistor TDR which generates the drive current IDR of a current value corresponding to a gradation signal SA[n]; and a light emission control switch SW1, which supplies the drive current IDR to the light-emitting element E in the light-emitting period of a time length specified by a light emission control signal SB[k]. The drive circuit 22[k] includes a first processing circuit 41, which outputs the gradation signal SA[n] corresponding to the gradation data D1[n] of the unit circuit U and the correction value A[n] of the unit circuit U, to each unit circuit U of the circuit group G[k], and a second processing circuit 42, which outputs the light emission control signal SB[k] that specifies the time length corresponding to the correction value B[k] of the circuit group G[k]. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a technique for controlling a light emitting element such as an organic EL (Electroluminescence) element.

  In a light emitting device in which a plurality of light emitting elements are arranged, an error in the light amount (gradation) of the light emitting elements becomes a problem. Patent Documents 1 and 2 disclose a technique for correcting a current value of a drive current supplied to a light emitting element according to an actual characteristic of each light emitting element. Patent Documents 1 and 3 disclose a technique for correcting a time length for supplying a drive current to a light emitting element according to an actual characteristic of each light emitting element.

JP 2005-103914 A JP-A-2005-81696 JP 2005-103816 A

  Incidentally, a plurality of drive circuits (for example, IC chips) may be used for driving each light emitting element. For example, in a light-emitting device (optical head) used in an electrophotographic image forming apparatus for exposure of an image carrier such as a photosensitive drum, a plurality of light-emitting elements arranged in a straight line are driven. A drive circuit is arranged along the arrangement of the light emitting elements.

  However, in the configuration using a plurality of drive circuits as described above, the characteristics of the drive circuit and the characteristics of the wiring connected to the drive circuit are different for each drive circuit. Therefore, even if the drive current is corrected in accordance with the characteristics of each light emitting element so that the light amounts of the respective light emitting elements match, the actual light quantity of the light emitting elements may be different for each drive circuit. In view of the above circumstances, an object of the present invention is to reduce an error in light amount of a light emitting element for each drive circuit.

  In order to solve the above problems, a light emitting device of the present invention includes a plurality of unit circuits, a plurality of drive circuits corresponding to each circuit group obtained by dividing the plurality of unit circuits, and a first correction value for each unit circuit. First storage means for storing, and second storage means for storing a second correction value for each circuit group, each of the plurality of unit circuits includes a light emitting element that emits light when supplied with a drive current, and a gradation signal A drive transistor that generates a drive current having a current value according to the light emission, and a light emission control switch that controls the supply of the drive current to the light emitting element in the light emission period specified by the light emission control signal. Each of the first signals outputs a gradation signal corresponding to the gradation specified for the unit circuit and the first correction value of the unit circuit to each unit circuit of the circuit group corresponding to the drive circuit. Each of the generation circuit and the circuit group corresponding to the drive circuit Relative position circuit, and a second signal generating circuit for outputting a light emission control signal specifying a time length corresponding to the second correction value of the circuit group.

  In the above configuration, in addition to the correction of the current value of the drive current according to the first correction value for each unit circuit, the time length of the light emission period according to the second correction value for each circuit group (for each drive circuit) is set. Correction is performed. Therefore, in addition to the light amount error between the light emitting elements in the circuit group, the light amount error of the light emitting elements between the circuit groups (that is, the light amount error of the light emitting elements for each drive circuit) can be reduced. is there.

  In a preferred aspect of the present invention, when the same gradation is specified for a unit circuit of one circuit group and a unit circuit of another circuit group among a plurality of circuit groups, the circuit in which the light amount of the light emitting element is one The second correction value of one circuit group and the second correction value of the other circuit group are individually set so that the group and the other circuit group match. In the above aspect, the light amount of each light emitting element can be sufficiently approximated (ideally matched) between one circuit group and another circuit group. Note that “the light amount of each light emitting element“ matches ”includes not only the case where the light amount of each light emitting element completely matches, but also the case where the light amount of each light emitting element substantially matches. Even if the light quantity of each light emitting element does not completely match, the light quantity of each light emitting element is substantially sufficient as long as the user of the image generated by the light emitting device does not recognize the difference in the light quantity of each light emitting element. It can be said that it matches.

  In a preferred aspect of the present invention, the second storage means includes a selection means for storing a plurality of second correction values for each circuit group and selecting any of the plurality of second correction values for each circuit group, The second signal generation circuit in each of the plurality of drive circuits outputs a light emission control signal that designates a time length according to the second correction value selected by the selection unit for the circuit group corresponding to the drive circuit. In the above aspect, since the second correction value applied to the generation of the light emission control signal is selected from a plurality of candidates, there is an advantage that the amount of light of each light emitting element can be easily controlled.

  In a preferred aspect of the present invention, each of the plurality of drive circuits is formed of a separate integrated circuit, and the first signal generation circuit outputs 1-bit first gradation data for instructing turning on or off of the light emitting element, A correction circuit that converts the second gradation data of a plurality of bits by correction using one correction value, and a D / A converter that generates a gradation signal from the second gradation data processed by the correction circuit. . In the above aspect, since 1-bit first gradation data is converted into a plurality of bits of second gradation data in the integrated circuit constituting the driving circuit, the second gradation data is generated externally. Therefore, the amount of data transferred to the drive circuit can be reduced as compared with the configuration in which the drive circuit is supplied to each drive circuit.

  The light emitting device according to the present invention is used in various electronic devices. A typical example of the electronic apparatus according to the present invention is an electrophotographic image forming apparatus in which the light emitting device according to each of the above embodiments is used for exposure of an image carrier such as a photosensitive drum. The image forming apparatus includes an image carrier on which a latent image is formed by exposure, a light emitting device of the present invention that exposes the image carrier, and a developer (for example, toner) added to the latent image on the image carrier. A developing device to be formed. However, the use of the light emitting device according to the present invention is not limited to the exposure of the image carrier. For example, a light-emitting device in which light-emitting elements are arranged in a matrix is used as a display device for various electronic devices such as a personal computer and a mobile phone.

1 is a block diagram of a light emitting device according to a first embodiment of the present invention. It is a block diagram of a circuit group and a drive circuit. It is a conceptual diagram for demonstrating correction | amendment of the light quantity of each light emitting element by a 1st processing circuit. It is a block diagram of a 1st processing circuit. It is a conceptual diagram for demonstrating correction | amendment of the light quantity of each light emitting element by a 2nd processing circuit. It is a block diagram of a 2nd processing circuit. It is a block diagram of the 2nd processing circuit in a 2nd embodiment. It is a conceptual diagram for demonstrating the light quantity of the light emitting element in 2nd Embodiment. It is a block diagram of the light-emitting device concerning a 3rd embodiment. It is a block diagram of a circuit group and a drive circuit according to a modification. It is a longitudinal cross-sectional view of an electronic device (image forming apparatus).

<A: First Embodiment>
FIG. 1 is a block diagram of a light emitting device 100 according to the first embodiment of the present invention. The light emitting device 100 is used in an electrophotographic image forming apparatus as an exposure device (optical head) that exposes an image carrier. As shown in FIG. 1, the light emitting device 100 includes a plurality of (K · N) unit circuits U formed on the surface of the substrate 10 and arranged in the X direction, and a drive circuit unit 20 that drives each unit circuit U. And a control circuit 30 for controlling the drive circuit unit 20 (K and N are natural numbers).

  The plurality of unit circuits U are divided into K circuit groups G [1] to G [K] with N adjacent units as a unit. The drive circuit unit 20 includes K drive circuits 22 [1] to 22 [K] corresponding to different circuit groups G [k] (k = 1 to K). The kth drive circuit 22 [k] drives N unit circuits U of the circuit group G [k] corresponding to the drive circuit 22 [k]. The drive circuits 22 [1] to 22 [K] are mounted on the surface of the substrate 10 in the form of an integrated circuit (IC chip). However, an embodiment in which K drive circuits 22 [1] to 22 [K] are configured by active elements (for example, thin film transistors) formed together with the unit circuits U on the surface of the substrate 10 is also employed.

  FIG. 2 is a block diagram of the circuit groups G [1] to G [K] and the drive circuits 22 [1] to 22 [K]. FIG. 2 representatively shows the kth circuit group G [k] and the drive circuit 22 [k]. As shown in FIG. 2, each unit circuit U of the circuit group G [k] includes a light emitting element E, a drive transistor TDR, a light emission control switch SW1, and a selection switch SW2. The drive transistor TDR, the light emission control switch SW1, and the selection switch SW2 are composed of, for example, an arbitrary conductive type thin film transistor formed on the surface of the substrate 10.

  The light emitting element E emits light when supplied with the driving current IDR. An organic EL element in which a light emitting layer of an organic EL material is interposed between the anode and the cathode is suitably employed as the light emitting element E. The drive transistor TDR controls the current value of the drive current IDR according to the potential of its gate.

  The light emission control switch SW1 is disposed on the path of the drive current IDR (between the drive transistor TDR and the light emitting element E in FIG. 2), and controls whether or not the drive current IDR can be supplied to the light emitting element E. The gate of the light emission control switch SW1 in each of the N unit circuits U in the circuit group G [k] is connected to the common control line 14 [k]. The selection switch SW2 is interposed between the gate of the driving transistor TDR and the signal line 12 [k] and controls the electrical connection (conduction / non-conduction) between them. The signal line 12 [k] and the control line 14 [k] are formed for each circuit group G [k] (for each drive circuit 22 [k]).

  As shown in FIG. 2, each of the drive circuits 22 [1] to 22 [K] includes a first processing circuit 41, a second processing circuit 42, and a selection circuit 44. The first processing circuit 41 of the drive circuit 22 [k] receives gradation signals SA [1] to SA [N] that specify the gradations of the N unit circuits U of the circuit group G [k] as signal lines. Output to 12 [k] in time division.

  The selection circuit 44 supplies selection signals SEL [1] to SEL [N] to the gate of the selection switch SW2 in each of the N unit circuits U of the circuit group G [k]. The selection signals SEL [1] to SEL [N] are alternatively set to the active level in a predetermined order. Specifically, the selection signal SEL [n] supplied to the nth unit circuit U in the circuit group G [k] is supplied with the gradation signal SA [n] to the signal line 12 [k]. The active level (the level at which the selection switch SW2 is turned on) is set during the period. Therefore, the gradation signal SA [n] is connected to the gate of the driving transistor TDR in the nth unit circuit U of the circuit group G [k] via the signal line 12 [k] and the selection switch SW2 of the unit circuit U. ] Is supplied. That is, the light emitting element E of the nth unit circuit U emits light with a luminance corresponding to the gradation signal SA [n].

  The characteristic FA1 in part (A) of FIG. 3 is that the driving current IDR generated by the driving transistor TDR is supplied over a predetermined time length when the gradation signals SA [1] to SA [N] are set to a common potential. In this case, the light quantity of each light emitting element E (that is, the light emission power corresponding to the time integral value of luminance) is meant. Since there is an error in the electrical or optical characteristics of each light emitting element E, even when the gradation signals SA [1] to SA [N] are set to a common potential, each light emission is as shown in the characteristic FA1. The light quantity of the element E does not completely match. Therefore, as described in detail below, the first processing circuit 41 of FIG. 2 has N unit circuits in the circuit group G [k] in which the light amount of each light-emitting element E when a common gradation is designated. The gradation signals SA [1] to SA [N] are generated so as to be approximated by U (ideally match).

  FIG. 4 is a block diagram of the first processing circuit 41 in each of the drive circuits 22 [1] to 22 [K]. In FIG. 4, the first processing circuit 41 of the kth driving circuit 22 [k] is representatively shown. As shown in FIGS. 1 and 4, the first processing circuit 41 of the drive circuit 22 [k] has gradation data D1 [1] that specifies the gradations of the N unit circuits U of the circuit group G [k]. ] To D1 [N] are sequentially supplied from the control circuit 30. The gradation data D1 [n] of one unit circuit U is 1-bit data instructing to turn on or off the light emitting element E in the unit circuit U.

  As shown in FIG. 4, each first processing circuit 41 of the drive circuits 22 [1] to 22 [K] includes a storage circuit 52 and a signal generation circuit 54. The memory circuit 52 of the first processing circuit 41 in the drive circuit 22 [k] is a set of N correction values A [1] to A [N] corresponding to the N unit circuits U of the circuit group G [k]. (Lookup table) is stored. A recording medium (for example, EEPROM) that stores the correction values A [1] to A [N] in a rewritable manner is suitable as the storage circuit 52, but a non-rewritable recording medium can also be adopted as the storage circuit 52.

  The signal generation circuit 54 in FIG. 4 generates the gradation signal SA [n] according to the gradation data D1 [n] and the correction value A [n]. As shown in FIG. 4, the signal generation circuit 54 includes a correction circuit 542 and a D / A converter 544. The correction circuit 542 generates gradation data D2 [n] by correcting the gradation data D1 [n] using the correction value A [n]. The gradation data D2 [n] is data that designates the current value of the drive current IDR (the potential of the gradation signal SA [n]) with a plurality of bits (for example, 10 bits). Specifically, the correction circuit 542 outputs the correction value A [n] as the gradation data D2 [n] when the gradation data D1 [n] indicates lighting of the light emitting element E, and the gradation data When D1 [n] instructs the light emitting element E to be turned off, gradation data D2 [n] (for example, a numerical value for setting the current value of the drive current IDR to zero) specifying the lowest gradation value is output. . The D / A converter 544 generates gradation signals SA [1] to SA [N] by sequentially D / A converting the gradation data D2 [1] to D2 [N] to generate the signal line 12 [ output to k].

  The characteristic FA2 in part (B) of FIG. 3 is obtained when the corrected gradation signals SA [1] to SA [N] using the correction values A [1] to A [N] are supplied to each unit circuit U. Means the light quantity of each light emitting element E. In part (B) of FIG. 3, the characteristic FA1 of part (A) is shown together with a broken line. As indicated by characteristic FA2, each of correction values A [1] to A [N] is gradation data after correction of gradation data D1 [1] to D1 [N] designating the same gradation (lighting). A drive current IDR corresponding to D2 [1] to D2 [N] (grayscale signals SA [1] to SA [N]) is supplied to N light emitting elements E of the circuit group G [k] over an equal time length. In this case, experimentally or statistically according to the relationship between the current and the light amount of each light emitting element E so that the light amount of the N light emitting elements E approximates (ideally matches) the target value LA. Selected. For example, the correction value A [n] of the light emitting element E having a smaller light amount when the drive current IDR having a predetermined current value is supplied is set to a larger value (that is, a value that increases the current value of the drive current IDR). The correction values A [k] to A [N] are set individually for each of the circuit groups G [1] to G [K], and then stored in each storage circuit of the drive circuits 22 [1] to 22 [K]. 52.

  As described above, by correcting the current value of the drive current IDR to which the correction values A [1] to A [N] are applied, the light quantity of the light emitting elements E of the N unit circuits U in the circuit group G [k] is reduced. It is possible to sufficiently suppress the difference (variation). However, there is an error in the electrical characteristics of the circuits and wirings in each of the drive circuits 22 [1] to 22 [N]. For example, the reference potential used by the D / A converter 544 to generate the gradation signals SA [1] to SA [N] depends on the position of each drive circuit 22 [k] (path length to which the reference potential is supplied). The drive circuits 22 [1] to 22 [N] may be different from each other. Therefore, even if the light amounts of the N light emitting elements E in the circuit group G [k] are sufficiently uniformed by the correction by the first processing circuit 41, as shown by the characteristic FB1 in the part (A) of FIG. The light quantity of the light emitting element E may be different in each of the circuit groups G [1] to G [K]. Therefore, in the present embodiment, the time length of the period during which the drive current IDR is supplied to the light emitting element E (hereinafter referred to as “light emitting period”) is individually adjusted for each circuit group G [k], so that the circuit group G [ 1] to G [K], the error of the light amount of the light emitting element E is reduced. As described in detail below, the second processing circuit 42 in the drive circuit 22 [k] of FIG. 2 sets the time length of the light emission period of the circuit group G [k] corresponding to itself to another circuit group G [k]. Adjust independently from.

  As shown in FIG. 2, the second processing circuit 42 of the drive circuit 22 [k] supplies the light emission control signal SB [k] to the control line 14 [k]. Therefore, a common light emission control signal SB [k] is supplied from the signal line 12 [k] to the gate of the light emission control switch SW1 in each of the N unit circuits U of the circuit group G [k]. When the light emission control switch SW1 is turned on by setting the light emission control signal SB [k] to the active level, the drive current IDR is supplied to the N light emitting elements E of the circuit group G [k]. On the other hand, when the light emission control signal SW [k] is set to the inactive level and the light emission control switch SW1 is turned off, the drive current IDR is supplied to the N light emitting elements E in the circuit group G [k]. Stop.

  As described above, each of the N light emitting elements E in the circuit group G [k] has a drive current IDR in a light emission period having a time length corresponding to the pulse width (duty ratio) of the light emission control signal SB [k]. Is supplied. That is, the light emission control signal SB [k] functions as a signal that specifies the time length of the light emission period of each light emitting element E of the circuit group G [k]. The light emission period is set within a period from the selection of the N unit circuits U by the selection circuit 44 to the start of the next selection.

  FIG. 6 is a block diagram of the second processing circuit 42 in each of the drive circuits 22 [1] to 22 [K]. In FIG. 6, the second processing circuit 42 of the kth drive circuit 22 [k] is representatively shown. As shown in FIGS. 1 and 6, the control circuit 30 sequentially applies K correction values B [1] to B [K] corresponding to different circuit groups G [k] to the drive circuits 22 [1] to 22 [1] to Supply to each of 22 [K]. The supply of the correction values B [1] to B [K] by the control circuit 30 is executed immediately after the light emitting device 100 is turned on, for example.

  As shown in FIG. 6, each of the second processing circuits 42 of the drive circuits 22 [1] to 22 [K] includes a storage circuit 62 and a signal generation circuit 64. The storage circuit 62 of the second processing circuit 42 of the drive circuit 22 [k] stores the correction value B [k] supplied from the control circuit 30. A rewritable recording medium is suitable as the storage circuit 62, but a recording medium that stores the correction value B [k] in an rewritable manner can also be adopted as the storage circuit 62.

  The signal generation circuit 64 generates a light emission control signal SB [k] having a pulse width (duty ratio) corresponding to the correction value B [k]. Accordingly, each of the N light emitting elements E in the circuit group G [k] is supplied with the drive current IDR over a light emission period having a time length corresponding to the correction value B [k]. Since the light amount of the light emitting element E is determined by the current value of the drive current IDR (the luminance of the light emitting element E) and the time length of the light emitting period, the light amount of each light emitting element E is corrected by the correction values B [1] to B [K ] For each circuit group G [k].

  The characteristic FB2 in the part (B) of FIG. 5 is obtained by correcting the current value of the drive current IDR in accordance with the correction values A [1] to A [N], in addition to the correction values B [1] to B [K]. It means the light quantity of each light emitting element E when the correction of the time length of the corresponding light emitting period is executed. In part (B) of FIG. 5, the characteristic FB1 of part (A) (when only the correction of the current value of the drive current IDR according to the correction values A [1] to A [N] is executed) is also shown with a broken line. Has been. As indicated by the characteristic FB2, each of the correction values B [1] to B [K] corresponds to each light emitting element E when the same gradation (lighting) is designated for each unit circuit U of the circuit group G [k]. For example, each of the drive circuits 22 [1] to 22 [K] is related so that the light quantity of K approximates (ideally matches) the target value LB in the K circuit groups G [1] to G [K]. It is selected experimentally or statistically according to the electrical characteristics. The correction value B [k] of the circuit group G [k] with a small amount of light from each light emitting element E when the gradation signal SA [n] of a predetermined potential is supplied has a larger numerical value (that is, the time length of the light emission period is increased). Numerical value).

  In the above embodiment, in addition to the correction of the current value of the drive current IDR according to the correction value A [k] (A [1] to A [N]) for each unit circuit U, for each circuit group G [k]. Correction of the time length of the light emission period according to the correction value B [k] (B [1] to B [K]) is executed. Therefore, not only the error in the light amount between the light emitting elements E in the circuit group G [K], but also the error in the light amount of the light emitting element E between the circuit groups G [k] (that is, for each drive circuit 22 [k]). It is also possible to reduce an error in the light amount of the light emitting element E).

<B: Second Embodiment>
Next, a second embodiment of the present invention will be described. In addition, about the element in which an effect | action and a function are equivalent to 1st Embodiment in each following form, the same code | symbol as the above is attached | subjected and each detailed description is abbreviate | omitted suitably.

  FIG. 7 is a block diagram of the second processing circuit 42 in the drive circuit 22 [k]. As shown in FIG. 7, the storage circuit 62 stores a plurality of correction values B [k] (B1 [k], B2 [k],...) For the circuit group G [k]. That is, the entire drive circuit unit 20 holds a plurality of second correction values B [k] for each of the circuit groups G [1] to G [K]. The selection circuit 66 selects one of a plurality of correction values B [k] (B1 [k], B2 [k],...) Stored in the storage circuit 62 in accordance with an instruction from the control circuit 30. The signal generation circuit 64 generates a light emission control signal SB [k] having a pulse width (duty ratio) corresponding to the correction value B [k] selected by the selection circuit 66 and outputs it to the control line 14 [k].

  For example, the control circuit 30 instructs the selection circuit 66 to specify the correction value B [k] according to various factors that affect image formation by the image forming apparatus. Factors affecting image formation include, for example, the speed of image formation (print quality) by the image forming apparatus, the type of paper used for image formation, the image density, or the temperature of the environment in which the image forming apparatus operates. There is. For example, the control circuit 30 instructs the correction value B [k] for each of the circuit groups G [1] to G [K] in accordance with an operation from the user who specifies the above conditions.

  As described above, the pulse widths of the light emission control signals SB [1] to SB [K] according to the correction value B [k] selected by the selection circuit 66 (the element groups G [1] to G [K] Since each light emission period) is set, the light quantity of each light emitting element E when the same gradation (lighting) is instructed to each light emitting element E is variably controlled. For example, as shown in FIG. 8, when the paper A is used, the light quantity of the light emitting element E of each circuit group G [k] is set to the target value L1, and when the paper B having a different property from the paper A is used, each circuit group. That is, the light amount of the light emitting element E of G [k] is set to the target value L2.

  In the above embodiment, the same effect as that of the first embodiment is realized. Furthermore, since the plurality of correction values B [k] are selectively applied to the selection of the time length of the light emission period of each circuit group G [k], it is possible to form an image suitable for actual use conditions. Note that the action of variably controlling the light amount of each light emitting element E according to the image forming conditions is achieved by, for example, correcting the correction values A [1] to A [N] stored in the storage circuit 52 of the first processing circuit 41. A configuration in which control is variably performed (hereinafter referred to as “proportional”) is also realized. However, in the comparison, it is necessary to store a set of N correction values A [1] to A [N] for each unit circuit U in the storage circuit 52 for each of a plurality of image forming conditions. There is a problem that the capacity required for the circuit 52 increases. In the second embodiment, a plurality of correction values B [k] specifying the time length of the light emission period (pulse width of the light emission control signal SB [k]) are held in the memory circuit 62 for each circuit group G [k]. Therefore, there is an advantage that the storage capacity required for the drive circuit unit 20 can be reduced (and the scale of the drive circuit unit 20 is further reduced) compared to the comparative example.

<C: Third Embodiment>
FIG. 9 is a block diagram of a light emitting device 100 according to the third embodiment of the present invention. The control circuit 30 includes a storage circuit 32 and a correction circuit 34. The storage circuit 32 stores N correction values A [1] to A [N] for each of the K circuit groups G [1] to G [K]. That is, the memory circuit 32 corresponds to an element obtained by merging the memory circuits 52 of the K drive circuits 22 [1] to 22 [K] in the first embodiment.

  The correction circuit 34 corrects the gradation data D1 [1] to D1 [N] and the circuit group G [k] in the storage circuit 32 for each of the K circuit groups G [1] to G [K]. The gradation data D2 [1] to D2 [N] are generated from the values A [1] to A [N]. The method for generating the gradation data D2 [k] from the gradation data D1 [k] and the correction value A [k] is the same as that of the correction circuit 542 of the first embodiment. The corrected gradation data D2 [1] to D2 [N] corresponding to the circuit group G [k] is supplied to the first processing circuit 41 of the drive circuit 22 [k]. The first processing circuit 41 of the drive circuit 22 [k] generates a gradation signal SA [n] by D / A conversion of the gradation data D2 [n]. The configuration and operation of the second processing circuit 42 are the same as in the first embodiment.

  In the above configuration, the first processing circuit 41 in each of the drive circuits 22 [1] to 22 [K] does not need the storage circuit 52 and the correction circuit 542 in FIG. There is an advantage that simplification of the configuration is realized. In the third embodiment, gradation data D2 [n] of a plurality of bits needs to be transferred from the control circuit 30 to each drive circuit 22 [k], whereas from the control circuit 30 in the first embodiment. Transferred to each drive circuit 22 [k] is 1-bit (lit / unlit) grayscale data D1 [n]. Therefore, from the viewpoint of reducing the amount of data transferred from the control circuit 30 to each drive circuit 22 [k] (further enabling reliable transfer), the first embodiment is preferable to the third embodiment. It is. Although the third embodiment has been described above based on the first embodiment, the configuration of the second embodiment that selectively applies a plurality of correction values B [k] is the same as that of the third embodiment. Applied.

<D: Modification>
Various modifications are added to the above embodiments. Specific modifications are exemplified below. Two or more aspects arbitrarily selected from the following examples may be merged.

(1) Modification 1
In the first embodiment and the second embodiment, the memory circuit 52 is arranged independently for each of the drive circuits 22 [1] to 22 [K]. However, each of a plurality (K · N) of unit circuits U is provided. A configuration in which the correction value A [n] is stored in a single storage circuit is also employed. The correction circuit 542 of the first processing circuit 41 in each of the drive circuits 22 [1] to 22 [K] generates the gradation signal SA [n] using the correction value A [n] in the storage circuit. . Similarly, a configuration in which the correction values B [1] to B [K] of the circuit groups G [1] to G [K] are stored in a single storage circuit is also employed. The signal generation circuit 64 of the second processing circuit 42 in each drive circuit 22 [k] generates a light emission control signal SB [k] corresponding to the correction value B [k] stored in the storage circuit. As understood from the above examples, the configuration in which the memory circuit 52 and the memory circuit 62 are independently arranged for each circuit group G [k] (for each drive circuit 22 [k]) is not essential in the present invention.

(2) Modification 2
In each of the above embodiments, the gradation signals SA [1] to SA [N] are supplied in time division to the N unit circuits U of the circuit group G [k]. However, as shown in FIG. A configuration is also adopted in which the first processing circuit 41 of the circuit 22 [k] outputs the grayscale signals SA [1] to SA [N] in parallel to the N unit circuits U of the circuit group G [k]. . In the configuration of FIG. 10, the selection switch SW2 of FIG.

(3) Modification 3
In each of the above embodiments, the light emitting device 100 suitable as an exposure device of the image forming apparatus has been exemplified. However, a light emitting device in which a plurality of unit circuits U (light emitting elements E) are arranged in a matrix may be used as a display device. Is possible. The second processing circuit 42 of the drive circuit 22 [k] generates the light emission control signal SB [k] for each row and outputs it to the light emission control switch SW1 of the unit circuit U for each row.

(4) Modification 4
The correction method using the correction values A [1] to A [N] is not limited to the above examples. For example, after correction by a predetermined calculation using gradation data D1 [n] and correction value A [n] (for example, addition / subtraction or multiplication / division between gradation data D1 [n] and correction value A [n]) A configuration for generating the grayscale data D2 [n] is employed. Therefore, the gradation data D1 [n] does not have to be one bit for designating one of lighting and extinguishing, and can be composed of a plurality of bits for designating any of a plurality of gradations.

(5) Modification 5
In the second embodiment, the selection circuit 66 is installed in each of the K drive circuits 22 [1] to 22 [K]. However, a configuration in which the control circuit 30 takes charge of the processing of the selection circuit 66 is also suitable. That is, the control circuit 30 stores a plurality of correction values B [k] (B1 [k], B2 [k],...) For each of the K circuit groups G [1] to G [K]. Any one of a plurality of correction values B [k] (B1 [k], B2 [k],...) Is instructed to the second processing circuit 42 of the drive circuit 22 [k] for each circuit group G [k]. Similar to the first embodiment, the signal generation circuit 64 of the second processing circuit 42 generates the light emission control signal SB [k] corresponding to the correction value B [k] instructed from the control circuit 30. As can be understood from the above examples, the “selection unit” in the present invention is a set of K selection circuits 66 installed for each drive circuit 22 [k] in the second embodiment, and in the fifth modification. This is a concept including both of the control circuit 30 and an element for selecting the correction value B [k] for each circuit group G [k].

(6) Modification 6
The organic EL element is only an example of the light emitting element E. For example, the present invention is applied to a light emitting device using a light emitting element such as an inorganic EL element or an LED (Light Emitting Diode) element as in the above embodiments. That is, the light-emitting element in the present invention is included as a driven element that emits light by supplying electric energy (typically, a current-driven self-light-emitting element).

<E: Application example>
Next, an electronic apparatus using the light emitting device according to the present invention will be described. FIG. 11 is a schematic diagram of an electronic apparatus (image forming apparatus) using the light emitting device 100 of each of the above forms as an exposure apparatus. The image forming apparatus is a tandem type full-color image forming apparatus, and the four light emitting devices 100 (100K, 100C, 100M, and 100Y) according to the above-described embodiments and the four photoconductors corresponding to the respective light emitting devices 100. And a drum 70 (70K, 70C, 70M, 70Y). Each light emitting device 100 is disposed so as to face an exposed surface 70 </ b> A (outer peripheral surface) of the photosensitive drum 70 corresponding to the light emitting device 100. Note that the subscripts “K”, “C”, “M”, and “Y” of each symbol are used to form each visible image of black (K), cyan (C), magenta (M), and yellow (Y). Means.

  As shown in FIG. 11, an endless intermediate transfer belt 72 is wound around a driving roller 711 and a driven roller 712. The four photosensitive drums 70 are arranged around the intermediate transfer belt 72 at a predetermined interval from each other. Each photosensitive drum 70 rotates in synchronization with driving of the intermediate transfer belt 72.

  In addition to the light emitting device 100, a corona charger 731 (731K, 731C, 731M, 731Y) and a developing unit 732 (732K, 732C, 732M, 732Y) are disposed around each photosensitive drum 70. The corona charger 731 uniformly charges the exposed surface 70A of the photosensitive drum 70 corresponding thereto. Each of the light emitting devices 100 exposes this charged surface 70A to be exposed, whereby an electrostatic latent image is formed. Each developing unit 732 forms a visible image (visible image) on the photosensitive drum 70 by attaching a developer (toner) to the electrostatic latent image.

  As described above, the visible images of the respective colors (black, cyan, magenta, yellow) formed on the photosensitive drum 70 are sequentially transferred (primary transfer) to the surface of the intermediate transfer belt 72 to form a full-color visible image. Is done. Four primary transfer corotrons (transfer devices) 74 (74K, 74C, 74M, and 74Y) are arranged inside the intermediate transfer belt 72. Each primary transfer corotron 74 electrostatically attracts a visible image from the corresponding photosensitive drum 70, thereby developing a visible image on the intermediate transfer belt 72 that passes through the gap between the photosensitive drum 70 and the primary transfer corotron 74. Transcript.

  The paper (recording material) 75 is fed one by one from the paper feed cassette 762 by the pickup roller 761 and conveyed to the nip between the intermediate transfer belt 72 and the secondary transfer roller 77. The full-color visible image formed on the surface of the intermediate transfer belt 72 is transferred (secondary transfer) to one side of the paper 75 by the secondary transfer roller 77 and is fixed to the paper 75 by passing through the fixing roller pair 78. . The paper discharge roller pair 79 discharges the paper 75 on which the visible image is fixed through the above steps.

  Since the image forming apparatus exemplified above uses an organic EL element as a light source, the apparatus is made smaller than a configuration using a laser scanning optical system. Note that the light emitting device 100 can also be applied to an image forming apparatus having a configuration other than those exemplified above. For example, a rotary development type image forming apparatus, an image forming apparatus that directly transfers a visible image from a photosensitive drum 70 to a sheet without using an intermediate transfer belt, or an image that forms a monochrome image. The light emitting device 100 can also be used for the forming apparatus.

  Note that the light-emitting device in which the light-emitting elements E are arranged in a matrix is also used as a display device for various electronic devices. Examples of the electronic device to which the present invention is applied include a portable personal computer, a mobile phone, a personal digital assistant (PDA), a digital still camera, a television, a video camera, a car navigation device, a pager, and an electronic notebook. , Electronic paper, calculators, word processors, workstations, videophones, POS terminals, printers, scanners, copiers, video players, devices with touch panels, and the like.

DESCRIPTION OF SYMBOLS 100 ... Light-emitting device, 10 ... Board | substrate, 12 [k] ... Signal line, 14 [k] ... Control line, 20 ... Drive circuit part, 22 [1] -22 [K] ... Drive circuit, 30 …… Control circuit, G [1] to G [K] …… Circuit group, U …… Unit circuit, E …… Light emitting element, TDR …… Drive transistor, SW1 …… Light emission control switch, SW2 …… Select switch , 41... First processing circuit, 42... Second processing circuit, 44... Selection circuit, 32, 52, 62... Storage circuit, 54 .. signal generation circuit, 542, 34. ... D / A converter, 64 ... signal generation circuit, 66 ... selection circuit.

Claims (5)

A plurality of unit circuits;
A plurality of drive circuits corresponding to each circuit group obtained by dividing the plurality of unit circuits;
First storage means for storing a first correction value for each unit circuit;
Second storage means for storing a second correction value for each circuit group;
Each of the plurality of unit circuits is
A light emitting element that emits light by supplying a driving current;
A drive transistor that generates the drive current having a current value corresponding to a gradation signal;
A light emission control switch for controlling the supply of the drive current to the light emitting element in a light emission period of a time length specified by the light emission control signal,
Each of the plurality of drive circuits includes:
A first signal that outputs a gradation signal corresponding to the gradation specified for the unit circuit and the first correction value of the unit circuit to each unit circuit of the circuit group corresponding to the drive circuit. A generation circuit;
A second signal generation circuit that outputs the light emission control signal for designating a time length corresponding to the second correction value of the circuit group for each unit circuit of the circuit group corresponding to the drive circuit. Light emitting device. When the same gradation is specified for a unit circuit of one circuit group and a unit circuit of another circuit group of the plurality of circuit groups, the light amount of the light emitting element is different from that of the one circuit group and the other circuit group. The light emitting device according to claim 1, wherein the second correction value of the one circuit group and the second correction value of the other circuit group are individually set so as to match with the circuit group. The second storage means stores a plurality of second correction values for each circuit group,
Selecting means for selecting one of the plurality of second correction values for each circuit group;
The second signal generation circuit in each of the plurality of drive circuits outputs the light emission control signal that specifies a time length according to a second correction value selected by the selection unit for a circuit group corresponding to the drive circuit. The light emitting device according to claim 1. Each of the plurality of drive circuits is composed of a separate integrated circuit,
The first signal generation circuit includes:
A correction circuit that converts 1-bit first gradation data instructing turning on or off of the light emitting element into second gradation data of a plurality of bits by correction using the first correction value;
The light-emitting device according to claim 1, further comprising: a D / A converter that generates the gradation signal from the second gradation data processed by the correction circuit. An electronic apparatus comprising the light-emitting device according to claim 1.

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